What is the biggest factor determining how q volcano will erupt?

The biggest factor determining how a volcano will erupt is the viscosity of the magma, which is influenced by its composition, temperature, and gas content. High-viscosity magma, often rich in silica, traps gases and leads to explosive eruptions, while low-viscosity magma allows gases to escape more easily, resulting in effusive eruptions. Additionally, the pressure buildup in the magma chamber and the presence of structural weaknesses in the volcano can also significantly affect the eruption style.